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  1. #include <iostream>
  2. #include <type_traits>
  3. #include <tuple>
  4. #include <array>
  5. using namespace std;
  6.  
  7. template<typename>
  8. struct TypeTeller;
  9.  
  10. template<typename T>
  11. void tellType(T t) { (void) TypeTeller<T>(); }
  12.  
  13. template<typename T>
  14. void tellType() { (void) TypeTeller<T>(); }
  15.  
  16. template<typename F, typename... Ts>
  17. struct runner
  18. {
  19. 	F f;
  20. 	tuple<Ts...> payload;
  21.  
  22. 	template<int I>
  23. 	static auto getRunner()
  24. 	{
  25. 		return +[](F& f, tuple<Ts...>& t) -> decltype(auto)
  26. 		{
  27. 			return f(std::forward<decltype(get<I>(t))>(get<I>(t)));
  28. 		};
  29. 	}
  30.  
  31. 	template<int... Ids>
  32. 	static auto generateRunnersHelper(std::integer_sequence<int, Ids...> is)
  33. 	{
  34. 		return std::array<decltype(getRunner<0>()), sizeof...(Ts)>{{ getRunner<Ids>()... }};
  35. 	}
  36.  
  37. 	static auto generateRunners()
  38. 	{
  39. 		return generateRunnersHelper(std::make_integer_sequence<int, sizeof...(Ts)>{});
  40. 	}
  41.  
  42. 	decltype(auto) run(int nth)
  43. 	{
  44. 		static auto runners = generateRunners();
  45. 		return runners[nth](f, payload);
  46. 	}
  47. };
  48.  
  49. template<typename F, typename... Ts>
  50. runner<F, Ts...> makeRunner(tuple<Ts...> t, F f)
  51. {
  52. 	return {f, t};
  53. }
  54.  
  55. int main() {
  56. 	auto t = make_tuple(42, "Dd", 3.14f);
  57. 	auto magic = makeRunner(t, [] (auto x) {
  58. 		cout << x << '\n';
  59. 	});
  60.  
  61. 	int n;
  62. 	while(cin >> n) magic.run(n); 
  63. 	return 0;
  64. }
Success #stdin #stdout 0s 3464KB
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2 0 1
stdout
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3.14
42
Dd
https://ideone.com/gi5Iwo
language:
C++14 (gcc 8.3)
created:
10 years ago
visibility:
public

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